The origin of the Pleistocene gravel in western Sichuan depression

Abstract：Combining related materials with regional geological mapping, the authors analyzed the cause for the formation of the Pleistocene gravel strata in the light of the space-time distribution and sedimentary features. The Pleistocene gravel strata are fan-shaped and have multi-level terrace. The Pleistocene gravel is genetically of fluvial deposition, as shown in such aspects as lithologic column structure, basic sequence and fabric characteristics. The authors also probed into the deposition epochs and the paleoclimate on the basis of ESR measurement, sporopollen and filling sequence. The results have led the authors to believe that there exist four sections of Pleistocene sequence which are not only related to each other in space but also have inheritance in deposition epochs and sedimentary features. It is thus concluded that the formation of the Pleistocene sequence was completed by the river from Longmen Mountain and the deposition was carried out in different epochs on the foreland basin under the condition of warm-humid climate. Finally，the authors made inversion for the regularity of the change of the Qingyi River in the foreland basin in Pleistocene.